In electrically driven windows such as power windows or electrically-operated sun roofs in automobiles, it is desirable that a safety device be provided which detects any foreign object (such as fingers, etc.) that becomes caught between the window and the window frame, and stops or reverses the motor that drives the window whenever such a foreign object is detected. Means for detecting such foreign objects include indirect-detection means for detecting the torque of the motor which changes when a foreign object becomes caught as described above, and direct-detection means, which detect the presence or absence of foreign objects by sensors installed in the window frame. Indirect-detection means suffer from problems such as a slow response speed; accordingly, Paragraph 118 of the FMVSS (U.S. Federal Motor Vehicle Safety Standards) uses direct-detection means. Piezoelectric cables and tape-form mechanical switches, consisting of a pair electrodes facing each other across a very small gap have been proposed as pressure sensors, which directly detect foreign objects. In the case of mechanical switches, foreign objects which are inserted obliquely between the window and the window frame may fail to be detected in some cases. On the other hand, as disclosed in Japanese Patent Application No. 61-226679, piezoelectric cables have a uniform directionality, and can therefore detect foreign objects without being affected by the angle of insertion. Furthermore, since piezoelectric cables have a coaxial structure, such cables are resistant to electromagnetic interference from the outside.
In regard to actual configurations of wire harnesses, a configuration in which a piezoelectric cable 4 is caused to extend along a window frame 2 of a vehicle door 1, and is further caused to extend from the window frame 2 to a motor control unit 3 accommodated in the lower part of the door 1 or in the vehicle body (not shown) is shown in FIG. 3; or a configuration in which a connector 5 is attached to the end portion of a piezoelectric cable 4' installed along the window frame 2, and the motor control unit 3 and connector 5 are connected to each other by a separate wire harness 8 which has connectors 6 and 7 installed at both ends is shown in FIG. 4.
However, in the case shown in FIG. 3, unwanted signals caused by vibration of the vehicle, may be picked up if there is any slack in the piezoelectric cable 4 in the lower part of the door 1. Although the problem of such signals can be solved by firmly fastening the piezoelectric cable so that slack is completely eliminated, such fastening of the cable 4 will result in additional cost.
Furthermore, in the case shown in FIG. 4, although no unwanted signals will be picked up in areas other than the window frame 2 where the cable 4 is supposed to act as a sensor, the addition of the connectors 6 and 7 results in an increase in the number of connections. This not only lowers the reliability of the connection, but also leads to an increase in parts and assembly costs as a result of the additional harness 8.